Can Teams Win By Taking Higher Quality Shots?

Shot quality is a hot-button issue among people who spend time trying to learn about the game of hockey through statistical analysis.

Intuitively, we all know that shot quality exists. A quick blast from center ice immediately prior to a line change is far less likely to score than a superstar taking a shot on a breakaway. The question, then, isn’t whether shot quality exists – we know it does – but whether teams can use it to help them win games.

Defensive shot quality is hard to measure because of goaltending effects. If Boston posts a better save percentage this season than Columbus, we can’t say that it’s strictly a matter of their team playing better defense or a brilliant coaching stratagem – because Tim Thomas and Steve Mason are very different goaltenders. Various methods of measuring shot location to split defensive performance from goaltending performance remain problematic and unproven.

That problem, however, doesn’t exist when we look at team offense. A team’s shooting percentage tells us exactly how likely they were to score on any given shot. Therefore, if certain teams in the league are better than others at taking quality shots, it’s something that should show up when we look at their records from year-to-year.

Naturally, we’d want to level the playing field – some teams get more power plays or penalty kills, some teams spend more time in 4-on-4 situations, etc. To get a really even idea of what teams are good at taking quality shots, we’d only want to look at 5-on-5 game play – it’s the most common situation, the area where coaching and overall team ability should be most evident.

If we go back to 2010-11, the best team in the league at converting their shots was the Philadelphia Flyers. In 2009-10… they were the 27th-best team in the league. The Capitals were the best team in the league in 2009-10, and they fell all the way to 23rd in 2010-11. In fact, the average finish of a team that leads the league in shooting percentage in the previous and prior years is 14th overall in the NHL. Interestingly, the average finish of a team that finishes last in the league in shooting percentage in the previous and prior years is also 14th overall.

Still, those are just examples. To really see if shot quality matters offensively, we’d want to look at the entire league, over a period of years. Thanks to Behind the Net, we can do that – we have four years of 5-on-5 shooting data, from 2007-08 to 2010-11. We’ll run mathematical correlations, to see the relationship from one year to the next – a score of 1 represents a perfect correlation, a score of zero shows no correlation whatsoever.

2007-08 to 2008-09 correlation: 0.179

2008-09 to 2009-10 correlation: -0.067

2009-10 to 2010-11 correlation: -0.121

Average year-to-year correlation: -0.003

The average correlation is actually slightly negative over these years, but it’s very, very close to exactly zero. In other words, there seems to be no connection between how good a team’s shooting percentage is from one year to the next. This is a significant argument that there is no major difference between individual NHL teams in their ability to score on any given shot – over the big picture, shot quality in 5-on-5 situations evens out.

While a team’s shot quality seems to bounce around erratically from year to year, the same is not true of the number of shots that they take. Here are the same correlations, but this time instead of looking at team shooting percentage, we will look at team shooting rates (shots/60) in 5-on-5 situations:

2007-08 to 2008-09 correlation: 0.578

2008-09 to 2009-10 correlation: 0.453

2009-10 to 2010-11 correlation: 0.462

Average year-to-year correlation: 0.498

That’s not a perfect correlation by any means, but there’s clearly a relationship between how teams perform from one year to the next – something we didn’t find when we looked at shot quality.

Because shot rates are at least somewhat predictable, we can view them as a team skill – teams that are good at this one year stand a good chance at being good at it the next year. Because shooting percentage is unpredictable (at the team level) it becomes very difficult to argue that certain teams are better at it than others.

1. Location fallacy: The assumption that location correlates directly with quality is specious.

It seems true in a ‘linear’ (FLOABTerm) sense, but it’s false.

A shot from centre ice is lower ‘quality’ than a shot from the slot. Agreed

However, a “whacking, whacking, whacking” from the top of the crease is three low quality shots from in close vs a two-on-one Stamkos slapper from the top of the circles.

What about screened shots from the point vs shots from the same spot with no screen? Shot quality vs “play” quality is/was evident in “garbage” goals/crashing the net.

This is Location fallacy. (related: it’s one of many reasons why we now coach goalies not to set their angle early, or too early. It’s better to drive quickly to the angle and establish, than to glide out early toward the puck carrier as the play develops)

2. Playing to the score. The assumption that Team A consistently takes the same ‘quality:skill’ shots throughout the game is also specious.

I think the same conclusion with shot volume may be true about quality. When the score is tied or early in the game, the more ‘skilled’ team A will likely get higher quality chances than the ‘unskilled’ team B. Think of All-star games… or Canada vs Norway games.

Once the score is out of reach, Team A will likely be more inclined to make the safe shot, even if it’s from in close, than the defenceman joining the rush 4 on 2 play. Returning to a position of protecting the lead and turning down the offence.

The “safe” shot is easier to save. Quality should spike and drop in correlation to playing to the score effects?

General concern: It’s dangerous to say “We think we can subjectively see it, but mathematically, we can’t find a strong correlation, therefore it probably doesn’t exist and our subjective eye is being deceived.”

At the risk of showing my age, there was an old chestnut that the Soviets were the masters of the “don’t shoot until you see the whites of their eyes” approach to offense. That is all shots were quality shots. I realize that stats keeping was not as detailed as it is today, but have you ever looked to see if the Soviets of the 70s did in fact only take “quality” shots? Example: The alleged “greatest game ever played” between Montreal Canadiens and Red Army on New Years Eve 1975 featured shots on goal of 35 to 13 respectively. So was Dryden’s 0.769 save % an indication that the Soviets were very patient and precise or Dryden “sieved” out. Not making a point just curious.

Edit: took a quick look at the 72 Summit Series. Canada outshot USSR in 6 of 8 games but not by crazy margins. Interestingly the Godless Commies . . . . er . . . our Soviet friends, lost both games that they outshot Phil, Paul and the fellas. That is the extent of my statistical analysis.

But clearly us aficionados know that Beta is a far superior system to VHS. No matter what those VHS troglodytes say about performance, efficacy and ubiquity we have the specs on our side! Long live Beta, the machine of technological erudition!!

Willis, I appreciate what you try to do with adding statistics to Hockey, but you really need to post your Descriptive Statistics and regression tests on known years to demonstrate causation along with correlation.

Have you stat buffs been doing that stuff for all the popular measures?

Please don’t take this post as a jump down anyones throat, just trying to understand what is going on behind the claims.

I understand how baseball statistical analysis works, but thats because you can break down 95% of interactions into a single interaction between player and measurement. Hockey is a much tougher bird to look at because there are 9 other players on the ice, different systems, 2 referees and a whole host of other factors that go into a single play. (Outside of shootout attempts)